Control electrode structure for crossed-field amplifier



United States Patent 3,450,938 CONTROL ELECTRODE STRUCTURE FORCROSSED-FIELD AMPLIFIER George K. Farney, New Providence, N.J.,assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of the Army Filed Mar. 2, 1966, Ser. No.533,126 Int. Cl. H01 25/34, 25/50, 1/20 U.S. Cl. 315-39.3 2 ClaimsABSTRACT OF THE DISCLOSURE This invention relates to crossed-fieldamplifiers, and more particularly to a cathode-control electrodestructure for crossed-field amplifier tubes.

My novel cathode-control electrode is used in crossedfield amplifiersthat operate from a DC power supply with heaterless cathodes. In thistype of amplifier no current is obtained from the cathode until an RFinput signal causes back bombardment of the cathode. The backbombardment of the cathode causes copious secondary emission current.The current will ordinarily continue to flow between cathode and anodeafter the termination of the RF input, and the tube will eitheroscillate or put out noise.

Prior to my invention no completely satisfactory means to cut-offcurrent in crossed-field amplifiers after termination of the RF inputhad been devised for crossedfield amplifiers having slow wave circuitsof many sections or for crossed-field amplifiers with high peak powercapabilities. My invention which basically comprises a segmented cathodeprovides highly elfective cut-off even for crossed-field amplifiershaving extremely high peak power capabilities and for crossed-fieldamplifiers having slow wave circuits consisting of many sections.

Therefore, an object of my invention is to provide means to cut-01fcurrent flow in crossed-field amplifiers at the termination of the RFinput.

Another object of my invention is to provide means to cut-off currentflow in crossed-field high power amplifiers at the termination of aninput pulse.

A further object of my invention is to provide means to cut-ofl currentflow, at the termination of the RF input, in crossed-field amplifiershaving slow wave circuits of many sections.

The above mentioned and other Objects of my invention will be apparentby reference to the following detailed description and accompanyingdrawing in which:

The single figure is a perspective of my invention as it is utilized inthe type of crossed-wave amplifier tube that has the cathode surroundingan inverted circular electric mode anode.

The single figure shows part of a well known type of crossed-fieldamplifier tube in which a circular shaped cathode 1 surrounds a circularanode slow wave structure 2. In this type of crossed-field amplifier aDC voltage (not shown) is normally applied between the anode and thecathode. The cathode is operated as a cold cathode, therefore no currentis obtained from the cathode until an RF input signal causes backbombardment of the cathode. This back "bombardment causes copioussecondary emission current. The current will ordinarily continue to flowbetween cathode and anode after the termination of the RF input and thetube will either oscillate or put out noise. For many applications ofcrossed-field amplifiers it is not only desirable but essential forproper operation that the cathode current be cut-oil at the terminationof an input pulse.

Prior to my invention no method for effectively cuttingotf current flowat the termination of an input pulse had been devised for crossed-fieldamplifiers having high power capabilities or for crossed-fieldamplifiers having slow wave circuits of many sections. The prior artmethods for cutting-olf current flow operate satisfactorily only ifutilized in relatively low power crossed-field amplifiers having alimited number of sections in their slow wave circuits. My invention canbe utilized with any type of crossed-field amplifier regardless of thepower capabilities of the amplifier or the number of sections in theslow wave circuit. Referring to the figure, my invention comprisesfabricating the cathode into the segments numbered 1. Cathodes ofcrossed-field amplifiers are normally fabricated as continuous rings orcylinders. At the termination of an RF input pulse, positive pulses areapplied between alternate segments 1 of the cathode "by means oftransformer 3. Any suitable coupling means other than transformer 3 mayof course be used. It is obvious that the positive cathode segmentsimmediately attract the electron current and cut-01f the cathode currentflow.

While my invention is shown as being used with a particular type ofcrossed-field tube it is obvious that it can be utilized with any typeof crossed-field tube. It should also be obvious that the cathode can bedivided into more than four segments provided that an even number ofsegments is maintained. Up to a point a larger number of segments willenhance cut-off control. 1

I claim:

1. A crossed-field amplifier tube comprising: a centrally located anodeslow wave structure; a cold cathode divided into an even number ofsegments surrounding said anode; and transformer means to apply a pulsedvoltage between alternate segments of said segmented cold cathode at thetermination of an input pulse to said amplifier.

2. A crossed-field amplifier as described in claim 1 wherein said numberof segments is greater than 2.

References Cited UNITED STATES PATENTS 2,784,346 3/1957 Dodds SIS-39.632,832,005 4/1958 Brown 313338 X 3,305,751 2/1967 Brown I.. 31539.51 X3,315,121 4/1967 Staats 315-39.51

HERMAN K. SAALBACH, Primary Examiner. S. CHATMON, JR., AssistantExaminer.

US. Cl. X.R. 313-338: 315-3951

